|Publication number||US7762140 B2|
|Application number||US 12/332,401|
|Publication date||Jul 27, 2010|
|Filing date||Dec 11, 2008|
|Priority date||Jan 10, 2008|
|Also published as||US20090178487|
|Publication number||12332401, 332401, US 7762140 B2, US 7762140B2, US-B2-7762140, US7762140 B2, US7762140B2|
|Inventors||Jared E. Girroir, Nicholas Moelders|
|Original Assignee||Sensata Technologies, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (7), Referenced by (1), Classifications (5), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
Benefit is claimed under 35 USC Section 119 (e) (1) of U.S. Provisional Application No 61/020,227, filed Jan. 10, 2008.
This invention relates generally to condition responsive fluid sensors and more particularly to combined fluid pressure and temperature sensors.
Fluid pressure responsive capacitive transducers comprising a variable capacitor mounted in a fluid chamber having a thin ceramic diaphragm exposed to the fluid so that a change in fluid pressure causes concomitant changes in the position of the diaphragm to thereby cause change in the capacitance of the capacitor are well known in the art. Transducers of this type are shown and described, for example, in U.S. Pat. No. 4,716,492, the subject matter of which is incorporated herein by this reference. In that patent, a thin ceramic diaphragm is shown mounted in closely spaced, sealed, overlying relation to a ceramic substrate. Metal coatings are deposited on opposing surfaces of the diaphragm and substrate to serve as capacitor plates arranged in predetermined closely spaced relation to each other to form a capacitor. Capacitor terminal pins having one end connected to the capacitor plates are mounted in bores extending through the substrate with opposite ends connected to signal conditioning circuitry disposed in an electric circuit chamber at an opposite face surface of the substrate. A connector body of electrical insulating material, received over the signal conditioning circuitry, mounts transducer terminals extending into the electric circuit chamber for connection to the signal conditioning circuitry. Capacitance is converted by the circuitry to an output voltage related to the fluid pressure. The capacitor is received in a suitable housing having a fluid receiving port and is provided with a fluid seal enabling the transducer to be used with fluid pressures up to 10,000 psi or higher.
In certain applications it is desirable to measure temperature of fluid as well as pressure. A combined pressure responsive transducer and temperature sensor is shown and described in U.S. Pat. No. 5,974,893, the subject matter of which is incorporated herein by this reference. In that patent a variable capacitor having a rigid substrate and a flexible diaphragm, each provided with a capacitor plate on a respective face surface, are attached to each other in aligned, overlying, spaced apart relation by a generally annular glass seal. The variable capacitor is disposed in a housing with the diaphragm exposed to fluid in a fluid pressure chamber of the housing that is in fluid communication with a fluid pressure receiving port of the housing. Electrical traces extend from the capacitor plates into an enclosed window in the glass seal for electrical connection with electrical pins extending through the substrate. A temperature responsive element is mounted for direct engagement with electrical leads that extend through an opening in the diaphragm near its outer periphery aligned with the glass seal.
Temperature sensor pins extend through the substrate and are connected to respective connection pads. The other ends of the temperature sensor pins, as well as the electrical pins for the variable capacitor, are connected to signal conditioning circuitry provided in an electric circuit chamber formed between the housing and a connector body attached to the housing. In one embodiment a temperature responsive element such as a thick film thermistor is coated onto the exposed face of the diaphragm along with electrically conductive traces connected to the connection pads. Other embodiments have the thermistor disposed within a fluid receiving port of the housing or disposed beyond the port with or without a protective sheath.
Each of the above embodiments of the U.S. Pat. No. 5,974,893 patent have certain limitations. With respect to the embodiment having the thermistor coated onto the exposed face of the diaphragm, it is desirable to reduce the response time of the temperature sensor and to provide a temperature sensor that has enhanced environmental compatibility, that is, a sensor that has greater immunity to the corrosivity of the media to which it is exposed. With regard to mounting the thermistor so that it is disposed within the fluid receiving port or at a location beyond the port, it is desired to provide a combined fluid pressure and temperature responsive sensor that is less costly to manufacture, one that is easier to assemble as well as one that is more robust while still having a short response time.
It is therefore an object of the present invention to provide a low cost, robust pressure and temperature sensor having an improved short period of response. Another object of the invention is the provision of such a sensor particularly adapted to measure pressure in the 6.5 psia to 1,000 psia range, and temperature in the −40 degree C. to 125 degree C. range for fluid applications. Yet another object of the invention is the provision of such a sensor that has superior environmental compatibility.
Briefly, in accordance with the preferred embodiment of the invention, a combined pressure responsive transducer and temperature sensor comprises a housing having a fluid pressure receiving port in fluid communication with a fluid pressure chamber. A variable capacitor having a rigid substrate and a flexible diaphragm are each provided with a capacitor plate on a respective face surface with the diaphragm attached to and spaced from the substrate and with the capacitor plates facing each other in aligned, spaced apart relation in a gap formed by a generally annular glass seal. The variable capacitor is disposed in the housing with the diaphragm exposed to the fluid pressure chamber. Electrical traces extend from the capacitor plates for connection with electrical pins extending through the substrate.
The opposite ends of the electrical pins are connected to signal conditioning circuitry disposed in an electric circuit chamber formed between the housing and the connector body which mounts transducer terminals also connected to the electric circuitry.
A temperature responsive element is mounted on the face surface of the diaphragm exposed to the fluid pressure chamber. First and second electric traces are connected to the temperature responsive element and extend along the diaphragm surface to and through openings in the diaphragm near its outer periphery aligned with the glass seal. According to a feature of the preferred embodiment of the invention, the temperature responsive element is a discrete SMT NTC (negative temperature coefficient of resistivity) thermistor placed on the diaphragm surface along with the electric traces and with a thin layer of polymer disposed over the diaphragm, the temperature responsive element and the first and second electric traces. The first and second electric traces extend through the openings in the diaphragm and are connected to other electrical pins extending through the substrate.
According to a further feature of the preferred embodiment, the temperature responsive element is positioned on the diaphragm so that it is aligned with the glass annular seal between the rigid substrate and the flexible diaphragm laterally beyond the active area of the diaphragm.
The fluid pressure receiving port comprises an open tubular member in fluid communication with the fluid pressure chamber and formed with an external thread for convenient installation in a fluid media system. A fluid flow diffuser received in the port has longitudinally extending walls separating the internal space of the tubular member into a passageway having a plurality of paths, preferably four, leading from a location external to the housing to the fluid pressure chamber. The fluid flow diffuser paths are oriented so that at least one is upstream relative to the fluid flow and serves as a path bringing fluid flow up to the fluid pressure chamber and across the temperature responsive element and at least one that is downstream that serves as a return path bringing the fluid back to the fluid media source.
Other objects, advantages and details of the novel and improved combined pressure and temperature sensor apparatus of the invention appear in the following detailed description of the preferred embodiment of the invention, the detailed description referring to the drawings in which:
A variable capacitor 14 having a substrate portion 14 a and a flexible diaphragm 14 b attached to the substrate in spaced apart, sealed relation is received in chamber 12 g of the housing with a fluid sealing gasket 16 of suitable material such as fluorosilicone forming a fluid pressure chamber 12 k with a face surface of diaphragm 14 b exposed to the fluid pressure chamber. Spacing of the ceramic sense element relative to the housing is controlled via the crimping process of tubular wall 12 d to be discussed (control of force/displacement).
An electrically insulative connector 20 has an end 20 a formed with a radially outwardly extending circumferential flange received in the open end so that attenuated wall 12 d of the housing can be deformed inwardly to clampingly engage the connector, as shown in
With particular reference to
As shown in
A fluid flow diffuser 30 of suitable material, such as plastic or metal, is disposed in fluid receiving port 12 b in order to improve fluid flow across the temperature responsive sensor to increase both the accuracy and the response time of the sensor. Fluid flow diffuser 30 comprises a fluid flow passage formed by longitudinally extending walls 32 a that extend from the bottom wall 12 h of the fluid pressure chamber down through the tubular port or coupling member to a location beyond first end 12 a of the housing and forming a plurality of paths, preferably four, so that regardless of orientation in the fluid flow, at least one path will face the upstream side of the fluid flow while at least one other path will face the downstream side. An end wall 32 b that lies in a plane generally perpendicular to the longitudinal axis, along with the opening of the port at 12 b serve as an entrance to an upstream first path 30 c (see arrows in
Thus the provision of protective layer 28 g allows the minimization of the thermal mass of the temperature sensor by obviating the need for a thick epoxy protective coating or the like and without concern of corrosivity of the fluid media. The provision of diffuser 30 results in optimum fluid flow of the media up to and across temperature sensor 28. These features provide faster response time of the temperature sensor with improved accuracy in a device that is robust and readily manufacturable.
The sensor functionality at the high and low ends of a particular application, for example, a range of Reynolds numbers 500 to 10000, is extremely sensitive to the geometry of the diffuser and coupling in which it is located. At low flow rates, e.g., Re 500, temperature response is poor so ideally a large diffuser and opening should be provided to divert a large amount of fluid up into the fluid pressure chamber 12 k. On the other hand, at high flow rates, e.g., Re 10000, pressure error due to the dynamic component of a dense flowing fluid requires a small diffuser for minimal flow disturbance. For the 500-10000 range of Reynolds numbers the optimum geometry of the sensor, with reference to
For another application, for example, for a small engine with lower oil flow rates, different diffuser/coupling geometry would need to be employed for optimum results.
The diffuser enables highly integrated temperature and pressure sensor technology independent of temperature sensor technology, i.e., NTC, PTC, RTD and the like, as well as pressure sensor technology, i.e., piezo-resistive, capacitive ceramic, piezo-resistive metal strain gauge. Minimization of the temperature sensor in conjunction with good thermal isolation provides improved temperature response time and good thermal accuracy in a device that is both reliable and robust.
It should be understood that although a preferred embodiment has been described by way of illustrating the invention, the invention includes all modifications and equivalents of the disclosed embodiment falling within the scope of the invention. For example the flow diffuser is shown defining a passageway having straight paths leading to and from the fluid pressure chamber, the passage could also be formed so that the paths are curved, such as helical, if desired, as long as the fluid is caused to flow across the temperature responsive sensor. It is also within the purview of the invention to increase thermal isolation of the capacitive sensor 14 from housing 12 by providing thermal insulation between the capacitor and the side wall of housing 12 by a sleeve of thermal insulative material or by increasing the diameter of the chamber 12 g and providing spacing fingers to position the capacitor. Further, it is also within the purview of the invention to use the flow diffuser with other technologies for temperature and pressure sensing, as noted in the above immediately preceding paragraph.
Although the invention has been described with regards to a specific preferred embodiment thereof, variations and modifications will become apparent to those of ordinary skill in the art. It is therefore the intent that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US3597974 *||Apr 20, 1970||Aug 10, 1971||Avco Corp||Fluidic temperature sensor for gas turbine engines|
|US4716492||May 5, 1986||Dec 29, 1987||Texas Instruments Incorporated||Pressure sensor with improved capacitive pressure transducer|
|US4982351||Nov 6, 1989||Jan 1, 1991||Texas Instruments Incorporated||Low cost high precision sensor|
|US5436795 *||Mar 28, 1994||Jul 25, 1995||Texas Instruments Incorporated||Pressure transducer apparatus and method for making same|
|US5486976 *||Nov 14, 1994||Jan 23, 1996||Texas Instruments Incorporated||Pressure transducer apparatus having a rigid member extending between diaphragms|
|US5499158 *||Nov 14, 1994||Mar 12, 1996||Texas Instruments Incorporated||Pressure transducer apparatus with monolithic body of ceramic material|
|US5974893||May 15, 1998||Nov 2, 1999||Texas Instruments Incorporated||Combined pressure responsive transducer and temperature sensor apparatus|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|EP2559987A2||Aug 17, 2012||Feb 20, 2013||Sensata Technologies, Inc.||Combination pressure/temperature in a compact sensor assembly|
|U.S. Classification||73/714, 361/283.4|
|Dec 11, 2008||AS||Assignment|
|May 18, 2011||AS||Assignment|
Owner name: MORGAN STANLEY SENIOR FUNDING, INC., NEW YORK
Free format text: SECURITY AGREEMENT;ASSIGNORS:SENSATA TECHNOLOGIES FINANCE COMPANY, LLC;SENSATA TECHNOLOGIES, INC.;SENSATA TECHNOLOGIES MASSACHUSETTS, INC.;REEL/FRAME:026304/0686
Effective date: 20110512
|Dec 30, 2013||FPAY||Fee payment|
Year of fee payment: 4